Search PubMed⌕ Search

Biomedical subjects

G M Thomas

Publications and source records attributed to G M Thomas.

At least 19 recordsLinked to original sources
PubMed2001

Phosphatidylinositol transfer proteins and protein kinase C make separate but non-interacting contributions to the phosphorylation state necessary for secretory competence in rat mast cells.

Mast cells permeabilized by streptolysin O undergo exocytosis when stimulated with Ca(2+) and guanosine 5'-[gamma-thio]triphosphate but become progressively refractory to this stimulus if it is delayed. This run-down of responsiveness occurs over a period of 20-30 min, during which the cells leak soluble and tethered proteins. We show here that withdrawal of ATP during the process of run-down is strongly inhibitory but that as little as 25 microM ATP can extend responsiveness significantly; this effect is maximal at 50 microM. When phosphatidylinositol transfer proteins (PITPs) are provided to cells at the time of permeabilization, run-down is retarded. We conclude that in the presence of ATP they convey substrates for phosphorylation that are essential for exocytosis and thus interact with the regulatory machinery. Furthermore, we show that PITPalpha and PITPbeta have additive effects in this mechanism, suggesting that they are not functionally redundant. Alternatively, secretion from run-down cells can be inhibited by the aminoglycoside antibiotic neomycin, which is understood to bind to phosphoinositide headgroups, and by a PH (pleckstrin homology) domain polypeptide that binds phosphoinositides. The apparent displacement of neomycin by exogenous PITPs suggests that these proteins screen essential lipids. Secretion from run-down cells is also inhibited by 1-O-hexadecyl-2-O-methyl-rac-glycerol (AMG-C(16)), an inhibitor of protein kinase C. The lack of synergy between neomycin and AMG-C(16) suggests that protein kinase C independently provides a second essential component through protein phosphorylation and that there are two independent phosphorylation pathways necessary for secretion competence.

Adenosine Triphosphate↗
PubMed2000

Preoperative chemo-radiation for carcinoma of the vulva with N2/N3 nodes: a gynecologic oncology group study.

PURPOSE: To determine if patients with carcinoma of the vulva, with N2/N3 lymph nodes, could undergo resection of the lymph nodes and primary tumor following preoperative chemo-radiation. METHODS AND MATERILAS: Fifty-two patients were entered in the study, but six patients did not meet the criteria of the protocol and were excluded. The remaining 46 patients are the subject of this report. Patients underwent a split course of radiation, 4760 cGy to the primary and lymph nodes, with concurrent chemotherapy, cisplatin/5-FU, followed by surgery. RESULTS: Four patients did not complete the chemo-radiation, because three expired and one refused to complete the treatment. Four patients who completed chemo-radiation did not undergo surgery, because two of them died of non-cancer-related causes, and in the other two patients, the nodes remained unresectable. Following chemo-radiation, the disease in the lymph nodes became resectable in 38/40 patients. Two patients who completed the course of chemo-radiation did not undergo surgery as per protocol because of pulmonary metastasis. One underwent radical vulvectomy and unilateral node dissection and the other radical vulvectomy only. The specimen of the lymph nodes was histologically negative in 15/37 patients. Nineteen patients developed recurrent and/or metastatic disease. The sites of failure were as follows: primary area only, 9; lymph node area only, 1; primary area and distant metastasis, 1; distant metastasis only, 8. Local control of the disease in the lymph nodes was achieved in 36/37 and in the primary area in 29/38 of the patients. Twenty patients are alive and disease-free, and five have expired without evidence of recurrence or metastasis. Two patients died of treatment-related complications. CONCLUSION: High resectability and local control rates of the lymph nodes were obtained in patients with carcinoma of the vulva with N2/N3 nodes treated preoperatively with chemo-radiation.

Adult↗
PubMed2000

Concurrent chemotherapy and radiation for locally advanced cervical cancer: the new standard of care.

Radical pelvic irradiation has constituted the definitive therapy for patients with large cervical cancers. No substantial improvements have been made in treatment outcomes. In the past year, however, a series of large, well-conducted randomized trials has evaluated the role of concurrent chemotherapy with pelvic irradiation in cervical cancer. These trials include definitive treatment of patients with stage IB2 to IVA disease and adjuvant treatment after radical surgery in stage IB2-IIA disease. Five trials have shown a consistent 30% to 50% reduction in the risk of death from disease when concurrent chemotherapy is used. Questions still remain as to what constitutes the best chemotherapy dose and schedule. In all of the positive trials, cisplatin was used, but three also used 5-fluorouracil. The level of survival improvement that occurs when chemotherapy is added to optimal irradiation and whether patients with stage IIIB and IVA benefit are also unclear. Improvements in survival rates for patients with solid tumors occur slowly. Based on the evidence, it is likely that concurrent chemotherapy with radiation will become the new standard of care for bulky and advanced cervix cancer.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2000

The Dictyostelium RasS protein is required for macropinocytosis, phagocytosis and the control of cell movement.

Endocytosis and cell migration both require transient localised remodelling of the cell cortex. Several lines of evidence suggest a key regulatory role in these activities for members of the Ras family of small GTPases. We have generated Dictyostelium cells lacking one member of this family, RasS, and the mutant cells are perturbed in endocytosis and cell migration. Mutant amoebae are defective in phagocytosis and fluid-phase endocytosis and are impaired in growth. Conversely, the rasS(-)cells show an enhanced rate of cell migration, moving three times faster than wild-type controls. The mutant cells display an aberrant morphology, are highly polarised, carry many elongated actin protrusions and show a concomitant decrease in formation of pinocytic crowns on the cell surface. These morphological aberrations are paralleled by changes in the actin cytoskeleton, with a significant proportion of the cortical F-actin relocalised to prominent pseudopodia. Rapid migration and endocytosis appear to be mutually incompatible and it is likely that RasS protein is required to maintain the normal balance between these two actin-dependent processes.

Animals↗
PubMed2000

[Effects of anemia and hypoxia on the course of tumors and the outcome of radiotherapy].

This paper will present an overview of the evidence that links anemia with a poor prognosis in a variety of human tumors treated with radiation, surgery, chemotherapy or combinations thereof. Hypoxia, acute or chronic in type, is also associated with a poor prognosis, mediated through two possible routes: 1) resistance to therapy with radiation or chemotherapy, and 2) the development of a more "aggressive" tumor phenotype. While anemia and hypoxia are related to some degree in some patients, it is probable that not all of the associated negative impact of anemia is translated through the hypoxia pathway. Because of the clinical importance and essential role hypoxia plays in tumor growth and treatment response, hypoxia and anemia are possible key targets for new therapies. The identified downstream molecular events resulting in increased glycolysis, erythropoiesis and angiogenesis form specific pathways which offer targets for inhibition. The relationship between anemia and hypoxia is complex and not clearly understood. Their relationships and the mechanisms by which they impact on treatment outcomes require further extensive investigations in both the clinic and laboratory.

Anemia↗
PubMed1999

The importance of hemoglobin levels during radiotherapy for carcinoma of the cervix.

BACKGROUND: It is unclear whether blood transfusion can overcome the negative impact of anemia before or during radiotherapy (RT) in patients with carcinoma of the cervix. The objective of this retrospective study was to examine the impact of anemia and blood transfusion on 605 patients with carcinoma of the cervix treated with radical RT at 7 centers across Canada in 1989, 1990, and 1992. METHODS: The data collected included hemoglobin (Hgb) levels from the time of diagnosis to the end of therapy; blood transfusions administered; and identifiable patient-, tumor-, and treatment-related factors. Survival, disease free survival, and pelvic control analyses were evaluated by univariate and multivariate analysis. RESULTS: The median follow-up was 41 months (range, 0-92 months). Presenting Hgb level, average weekly nadir Hgb (AWNH) during RT, and blood transfusion were correlated significantly with local control, disease free survival, and overall survival on univariate analysis. However, the AWNH remained significant on multivariate analysis, whereas Hgb at presentation and blood transfusion did not. The 5-year survival was 74% for patients with an AWNH >/= 120 g/L, 52% for patients with AWNH levels 110-119 g/L inclusive, and 45% for patients with AWNH levels < 110 g/L (P < 0.0001). At each Hgb level, patients who were transfused and maintained a specific Hgb level had a survival rate that was not significantly different from patients who were at that level spontaneously. There was a significant reduction in both pelvic and distant recurrence (P < 0.0001 and P < 0.0006, respectively) in patients whose AWNH level during RT was >/= 120 g/L compared with < 120 g/L. A reduction in the rate of distant recurrence was observed in patients with and without pelvic recurrence. CONCLUSIONS: AWNH is highly predictive of outcome for patients treated with RT for carcinoma of the cervix. Blood transfusion appears to overcome the negative prognostic effects of low presenting Hgb levels and AWNH levels.

Adenocarcinoma↗
PubMed1999

A GSK3-binding peptide from FRAT1 selectively inhibits the GSK3-catalysed phosphorylation of axin and beta-catenin.

The Axin-dependent phosphorylation of beta-catenin catalysed by glycogen synthase kinase-3 (GSK3) is inhibited during embryogenesis. This protects beta-catenin against ubiquitin-dependent proteolysis, leading to its accumulation in the nucleus, where it controls the expression of genes important for development. Frequently rearranged in advanced T-cell lymphomas 1 (FRAT1) is a mammalian homologue of a GSK3-binding protein (GBP), which appears to play a key role in the correct establishment of the dorsal-ventral axis in Xenopus laevis. Here, we demonstrate that FRATtide (a peptide corresponding to residues 188-226 of FRAT1) binds to GSK3 and prevents GSK3 from interacting with Axin. FRATtide also blocks the GSK3-catalysed phosphorylation of Axin and beta-catenin, suggesting a potential mechanism by which GBP could trigger axis formation. In contrast, FRATtide does not suppress GSK3 activity towards other substrates, such as glycogen synthase and eIF2B, whose phosphorylation is independent of Axin but dependent on a 'priming' phosphorylation. This may explain how the essential cellular functions of GSK3 can continue, despite the suppression of beta-catenin phosphorylation.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Stress-activated protein kinase-3 interacts with the PDZ domain of alpha1-syntrophin. A mechanism for specific substrate recognition.

Mechanisms for selective targeting to unique subcellular sites play an important role in determining the substrate specificities of protein kinases. Here we show that stress-activated protein kinase-3 (SAPK3, also called ERK6 and p38gamma), a member of the mitogen-activated protein kinase family that is abundantly expressed in skeletal muscle, binds through its carboxyl-terminal sequence -KETXL to the PDZ domain of alpha1-syntrophin. SAPK3 phosphorylates alpha1-syntrophin at serine residues 193 and 201 in vitro and phosphorylation is dependent on binding to the PDZ domain of alpha1-syntrophin. In skeletal muscle SAPK3 and alpha1-syntrophin co-localize at the neuromuscular junction, and both proteins can be co-immunoprecipitated from transfected COS cell lysates. Phosphorylation of a PDZ domain-containing protein by an associated protein kinase is a novel mechanism for determining both the localization and the substrate specificity of a protein kinase.

Amino Acid Sequence↗
PubMed1998

Preoperative chemoradiation for advanced vulvar cancer: a phase II study of the Gynecologic Oncology Group.

PURPOSE: To determine the feasibility of using preoperative chemoradiotherapy to avert the need for more radical surgery for patients with T3 primary tumors, or the need for pelvic exenteration for patients with T4 primary tumors, not amenable to resection by standard radical vulvectomy. METHODS AND MATERIALS: Seventy-three evaluable patients with clinical Stage III-IV squamous cell vulvar carcinoma were enrolled in this prospective, multi-institutional trial. Treatment consisted of a planned split course of concurrent cisplatin/5-fluorouracil and radiation therapy followed by surgical excision of the residual primary tumor plus bilateral inguinal-femoral lymph node dissection. Radiation therapy was delivered to the primary tumor volume via anterior-posterior-posterior-anterior (AP-PA) fields in 170-cGy fractions to a dose of 4760 cGy. Patients with inoperable groin nodes received chemoradiation to the primary vulvar tumor, inguinal-femoral and lower pelvic lymph nodes. RESULTS: Seven patients did not undergo a post-treatment surgical procedure: deteriorating medical condition (2 patients); other medical condition (1 patient); unresectable residual tumor (2 patients); patient refusal (2 patients). Following chemoradiotherapy, 33/71 (46.5%) patients had no visible vulvar cancer at the time of planned surgery and 38/71 (53.5%) had gross residual cancer at the time of operation. Five of the latter 38 patients had positive resection margins and underwent: further radiation therapy to the vulva (3 patients); wide local excision and vaginectomy necessitating colostomy (1 patient); no further therapy (1 patient). Using this strategy of preoperative, split-course, twice-daily radiation combined with cisplatin plus 5-fluorouracil chemotherapy, only 2/71 (2.8%) had residual unresectable disease. In only three patients was it not possible to preserve urinary and/or gastrointestinal continence. Toxicity was acceptable, with acute cutaneous reactions to chemoradiotherapy and surgical wound complications being the most common adverse effects. CONCLUSION: Preoperative chemoradiotherapy in advanced squamous cell carcinoma of the vulva is feasible, and may reduce the need for more radical surgery including primary pelvic exenteration.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1998

A randomized study of two doses of abdominopelvic radiation therapy for patients with optimally debulked Stage I, II, and III ovarian cancer.

PURPOSE: To determine whether an increased dose of abdominal radiation therapy results in improved disease control and survival in patients with early ovarian cancer. METHODS AND PATIENTS: Between 1981 and 1990, 125 patients with optimally debulked Stage I, II, and III ovarian cancer were entered into a prospective randomized clinical trial of abdominopelvic radiation therapy. Patients were stratified and randomized to either the control arm, treated with an abdominal dose of 22.5 Gy in 22 fractions, or the experimental arm of 27.5 Gy in 27 fractions. A pelvic boost dose of 22.5 Gy was used in both arms. There were 43 patients with Stage I tumors, 71 Stage II tumors, and 11 Stage III tumors. Nineteen patients had grade 1 histology, 77 grade 2, and 29 grade 3. Three patients had small-volume residual disease (<2 cm) in the pelvis alone and the remainder had no gross tumor following surgery. Median follow-up was 6.6 years (range 1.4-9.9). RESULTS: Overall survival (OS) at 5 years was 83% in the low-dose arm and 72% in the high-dose arm (p = 0.3). Disease-free survival (DFS) at 5 years was 74% and 67% in the low-dose and high-dose arms, respectively (p = 0.5). The difference in OS between the two arms was -11%, with 95% confidence intervals of -26% (favoring low-dose treatment) to 4% (in favor of high dose). The difference in DFS was -7% (95% confidence interval, -23 to 9%). Failure in the pelvis alone predominated (n = 15); six patients had abdominal and pelvic failure and seven patients failed in the abdomen alone. There were no differences in patterns of relapse, hematologic toxicity, or late complications between the two arms. Serious bowel toxicity was seen in three patients: two in the low-dose and one in the high-dose arm. A Cox proportional hazards model was used to assess the effect of treatment when adjusting for other prognostic variables. Ascites (p = 0.03, relative risk 2.05) was the only significant covariate in predicting disease-free survival, but was not prognostic for overall survival. CONCLUSIONS: There was no difference in survival, tumor control, or toxicity between high-dose and low-dose abdominopelvic radiation therapy. High-dose abdominopelvic radiation therapy is unlikely to be associated with an increase in OS of more than 4% or DFS of more than 9%.

Adult↗
PubMed1998

Examination of the role of ADP-ribosylation factor and phospholipase D activation in regulated exocytosis in chromaffin and PC12 cells.

The possible role of ADP-ribosylation factor (ARF)-activated and constitutive phospholipase D (PLD) activity in regulated exocytosis of preformed secretory granules in adrenal chromaffin and PC12 cells was examined. With use of digitonin-permeabilised cells, the effect of GTP analogues and exogenous ARF1 on PLD activity was determined. No evidence was seen for ARF-stimulated PLD activity in these cell types. Exocytosis from cytosol-depleted permeabilised chromaffin cells was not increased by adding recombinant nonmyristoylated or myristoylated ARF1, and exocytosis from both cell types was resistant to brefeldin A (BFA). Addition of bacterial PLD with demonstrably high activity in permeabilised chromaffin cells did not increase exocytosis in cytosol-depleted chromaffin cells. Diversion of PLD activity from production of phosphatidic acid (PA) due to the presence of 4% ethanol did not inhibit exocytosis triggered by Ca2+ or poorly hydrolysable GTP analogues in permeabilised chromaffin or PC12 cells. These results indicate that exocytosis in these cell types does not appear to require a BFA-sensitive ARF and the triggering of exocytosis does not require PLD activity and formation of PA. These findings rule out a general requirement for PLD activity during regulated exocytosis.

ADP-Ribosylation Factor 1↗
PubMed1998

Inhibition of virus-encoded thymidine kinase suppresses herpes simplex virus replication in vitro and in vivo.

Both herpes simplex virus type 1 (HSV-1) and HSV-2 encode a thymidine kinase enzyme which differs from cellular thymidine kinase in substrate specificity. Viral thymidine kinase enables the virus to replicate in cells that lack cellular thymidine kinase, namely those of the sensory neurons where the virus establishes, and periodically reactivates from, a latent state. Thymidine kinase-dependent HSV replication following viral reactivation at the site of latency is thought to precede the emergence of virus at mucosal surfaces. The ability to inhibit such an essential viral enzyme would potentially prevent HSV from replicating within neuronal tissue, and thus stop the recurrent disease cycle. Ro 32-2313 was designed as a selective and competitive inhibitor of HSV thymidine kinase and in vitro studies have confirmed this mechanism of action. In vivo evaluation of a soluble prodrug of Ro 32-2313, Ro 32-4397, was undertaken in murine models where pathogenesis was dependent upon viral replication in neuronal tissue. It was shown that in vivo administration of Ro 32-4397 (i) significantly reduced the viral titre detected in isolated dorsal root ganglia; (ii) prevented HSV-2-induced lethality in a systemic infection model; and (iii) reduced zosteriform lesion development in a model of dermal infection. Administration of Ro 32-4397 produced dose-related changes in viral pathogenicity towards those of the phenotype of a thymidine kinase-deficient virus. Overall, the study confirmed that thymidine kinase inhibitors can suppress the replication of HSV in vivo, and suggest that such inhibitors may reduce reactivation of the virus from latency if used prophylactically in recurrent HSV infection.

Animals↗
PubMed1997

An interunit performance improvement program: can you get me to the OR on time?

To maximize clinical outcomes of patients served and to efficiently use resources, delays contributing to patients' readiness for surgery and delays in surgery start times were identified as performance improvement measures that were monitored and evaluated. Because delays in patient readiness for surgery impact negatively on operating room use and length of stay, an interdepartmental multi-disciplinary approach was taken to measure performance. Data collection tools were developed to capture unit specific information on patients undergoing ophthalmic surgery. Design of the data collection tools, the data collection process, outcomes, and corrective actions will be discussed in this article.

Appointments and Schedules↗